Energies of interaction, vibrational frequency shifts, intermolecular vibration frequencies, and infrared intensity changes, all of them resulting from bringing two molecules together to form a one-to-one complex, have been calculated using the Pople-Beveridge-Dobosh INDO approximate quantum-mechanical $treatment,^{1}$ for a number of different ``complexes” in some different geometrical configurations. Calculations are restricted to the treatment of molecules composed of atoms from the first row of the periodic table, but the calculations for $H_{3}N-F_{2}$, for example, provide a good model for the interactions between amines and $I_{2}$. The extent of charge transfer from $NH_{3}$ to $F_{2}$, for example, has been calculated and the calculated charge distribution compared with that expected from simpler charge transfer theory and from experimental results in $I_{2}$ complexes. The relationship between the extent of charge transfer and the frequency shift of the halogen-halogen stretching vibration, suggested empirically by Friedrich and $Person,^{2}$ has been tested for these model systems. Calculations have been made for model systems including: $NH_{3}$ with $F_{2}$, $NH_{3}$ with $H_{2}$ (two different orientations), $NH_{3}$ with $N_{2}$ (two different orientations), and the water dimer. These results provide a rather complete theoretical model for understanding changes, both in frequency and in intensity, of vibrational spectra of molecules as they interact to form complexes.

Description:

This work was supported by the National Science Foundation, Research Grants No. GP-8111 and GP-17818. Additional support from the University of Florida Computer Center and the College of Liberal Arts and Sciences is gratefully acknowledged. $^{1}$J. A. Pople, D. I. Beveridge and P. A. Dobosh, J. Chem. Phys., 47, 2026 (1967): CNINDO: CNDO and INDO Molecular Orbital Program, by P. A. Dobosh, Quantum Chemistry Program Exchange, University of Indiana, No. 141. $^{2}$H. B. Friedrich and W. B. Person, J. Chem. Phys., 44, 2161 (1966).""Author Institution: Department of Chemistry, University of Florida

URI:

http://hdl.handle.net/1811/8392

Other Identifiers:

1970-D-3

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